WILMINGTON, Del. -- Democrats are divided this year not by the issues but by a feeling and a theory.

This helps explain why the preferences of voters in the Democratic presidential primaries so far have gyrated so wildly. In the absence of deep divisions on policy, Democrats have been cut loose from their ideological moorings. Philosophical unity has bred new forms of conflict.

Barack Obama has surged to rough parity with Hillary Clinton in the national polls not because Democrats reject her carefully thought-out solutions to the central public problems but because he has created in the party's rank and file a feeling of liberation -- from intimidation by Republicans, from old divisions, from history itself.

At a packed rally in a downtown square here on Sunday, emblematic of Obama's appearances around the country, the candidate drew the usual applause for the usual Democratic applause lines on the infamy of the Bush administration, the urgency of universal health care and the unfairness of Republican economic policies.

But he connected most when he spoke of his willingness to oppose the Iraq war when many, including Clinton, didn't. This marked his liberation from Republican bullying on national security. He spoke of the surge of young people into politics and the extraordinary levels of participation in the Democratic primaries. This spoke to his party's desire to be liberated from the old math of the Reagan era.

And on it went: He noted the multitude he drew to a rally in Boise, Idaho, of all places (liberation from the old electoral map); the support he has won from Republicans (liberation from divisiveness); and his determination to govern "not by the polls but by principle" (liberation from calculation and, to some, from Clintonism).

All this strikes Hillary Clinton's supporters as terribly unfair. Some liberals who support Obama acknowledge privately that many of her positions on domestic issues are more carefully crafted and in some respects more liberal than his.

Her steadfastness in supporting a requirement that all Americans buy health insurance is instructive. Clinton is right that universal coverage will require a mandate of some sort. Obama's political attacks on the mandate are not only wrong, they may set back the future prospects of health-care reform by feeding ammunition to its opponents.

One piece of Obama campaign literature looks suspiciously similar to the "Harry and Louise" ads run in the 1990s by the health insurance industry against the Clinton health plan. The Obama ad depicts a concerned young couple and charges: "Hillary's plan forces everyone to buy insurance, even if you can't afford it."

Gene Sperling, a Hillary Clinton economic adviser, says he's disappointed in Obama, whom he generally likes. "I'd rather be in the tradition of Harry Truman, who supported universal coverage," he said, "than in the tradition of Harry and Louise."

But even on this issue, Clinton's advantage is undercut by her repeated refusal -- on display Sunday on ABC's "This Week" -- to specify the penalty she'd impose on those who failed to buy health insurance. Her reticence underscores the political challenge of supporting mandates of any kind.

The larger difference between Clinton and Obama is in their respective theories of change. Implicit in the Clinton narrative, as she put it on the stump last weekend, is the idea that "making change is hard." Only someone with carefully laid plans and the toughness to go toe-to-toe with the Republicans in the daily and weekly Washington slog can hope to achieve reform.

Obama agrees to an extent. "I know how hard change is," he says. But he promises to transcend the old fights -- the liberation narrative again -- by building a "bottom-up" movement to create inexorable pressure for reform that would draw in even Republicans.

"Good intentions are not enough," he said in his Wilmington speech. They need to be "fortified with political will or political power." Obama marries a softer rhetorical line on Republicans with a more far-reaching and activist analysis of how change happens. He thus manages to go to Clinton's right and left at the same time.

That's why Obama is on the move in a way that worries Clinton's lieutenants. She promises toughness, competence, clarity and experience in a year when many Democrats are seeking something closer to salvation.

One of the politicians who spoke before Obama at the rally, Delaware state Treasurer Jack Markell, cited the New Testament letter to the Hebrews in which Saint Paul spoke of "the substance of things hoped for, the evidence of things not seen." It was a revealing moment: While Clinton wages a campaign, Obama is preaching a revival.